A lithium nonaqueous electrolyte battery has been widely used as a battery with a high energy density in various fields such as electric vehicles, power storage and information devices. In accordance with this, there are increasing requests from the market for nonaqueous electrolyte batteries, and studies have been actively conducted.
Among them, there is a request for a high energy density, that is, a large discharge capacity per unit mass or unit volume of a lithium nonaqueous electrolyte battery, which is used as a power source for an electric vehicle, in terms of its application. Further, there is a request for a battery to be capable of efficiently performing charge even in a case in which a high current is instantly input to the battery in order to recover the kinetic energy produced at the time of deceleration. Further, there is a request for a battery to enable high output, that is, to be capable of instantly discharging a high current, conversely, at the time of start, at the time of rapid start, and at the time of rapid acceleration or the like. That is, there is a demand for a secondary battery as a power source for an electric vehicle to have favorable input and output characteristics in a short period of time as well as a large capacity.
A carbon-based material has been widely used as a negative electrode active material of this lithium nonaqueous electrolyte battery. Recently, however, a focus has been placed on a spinel-type lithium titanate, which has a higher Li inserting-and-extracting potential as compared to the carbon-based material. There is no change in volume accompanying charge and discharge reactions in this spinel-type lithium titanate, which is excellent in cycle characteristics. In addition, this spinel-type lithium titanate has a higher stability as compared to the carbon-based material since there is a low possibility of generation of lithium dendrites, and further, has a great advantage that thermal runaway is hardly caused since the lithium titanate is ceramic.
On the other hand, a nonaqueous electrolyte battery which uses a spinel-type lithium titanate as the negative electrode active material has a problem that an energy density is low, and accordingly, there is a request for a negative electrode material with which a high capacity can be obtained. Thus, studies have been conducted regarding a niobium titanium composite oxide such as Nb2TiO7 which has a larger theoretical capacity per mass than the spinel-type lithium titanate, Li4Ti5O12.